Whole blood is made up of various cellular components such as red cells, white cells and platelets suspended in its liquid component, plasma. Whole blood can be separated into its constituent components (cellular or liquid), and the separated component can be administered to a patient in need of that particular component. For example, platelets can be removed from the whole blood of a healthy donor, collected, and later administered to a cancer patient, whose ability to make platelets has been destroyed by chemotherapy or radiation treatment.
Most commonly, platelets are collected by continuously or intermittently introducing whole blood from a donor into a centrifuge chamber wherein the whole blood is separated into its constituent components, including platelets, based on the densities of the different components. In the separation of platelets, sometimes referred to as plateletpheresis, the platelets are often concentrated to form a layer of packed platelets with some residual plasma (hereinafter "platelet concentrate"). For storage and/or transfusion to the patient, however, the platelet concentrate must be resuspended in a liquid medium, such as plasma.
There are several commercially available devices useful in the separation and collection of platelets. One such device is the CS-3000.RTM. Plus Blood Cell Separator, made by Baxter Healthcare Corporation of Deerfield, Ill. The Baxter CS-3000.RTM. Plus is an automated continuous flow centrifuge capable of performing numerous blood separation procedures, including plateletpheresis.
In a plateletpheresis procedure on the CS-3000.RTM. Plus, platelets are separated from whole blood in two "stages". In a first stage, red blood cells and white blood cells are separated from platelets and plasma. The separated red blood cells and white blood cells are returned to the donor and the platelets and plasma ("platelet-rich plasma") proceed to the second stage for further processing. In a second stage, the platelet-rich plasma is separated into plasma depleted of platelets (platelet-poor plasma) and a platelet concentrate, which as defined above, includes platelets and residual plasma. Most of the plasma is returned to the donor, but some remains with the platelet concentrate. At the completion of the platelet collection, the platelet concentrate is then resuspended by mixing the platelet concentrate with an additional amount of plasma. After the platelets have resuspended, they may be transfused to a patient.
Another device useful in plateletpheresis is the AMICUS.TM. Separator--also an automated continuous flow blood cell separator made by Baxter Healthcare Corporation. In the AMICUS.TM., red blood cells and white blood cells are also separated from platelet-rich plasma in a first stage and the platelet-rich plasma is then separated into platelet poor plasma and platelet concentrate in a second stage. The collected platelet concentrate is also resuspended in additional plasma.
In addition to the automated procedures described above, platelets can also be collected on systems where the donor is not connected to the instrument during the plateletpheresis procedure. In these "manual" systems, whole blood is collected from a donor. The container of collected whole blood is then centrifuged to separate the platelet rich plasma in a first stage from the other components. In a second stage of the procedure, platelets are separated from plasma to form a platelet concentrate. The platelet concentrate is then resuspended in a liquid, such as plasma.
Although plasma is effective for resuspending platelets, it may not be the ideal medium for platelet resuspension for several reasons. First, plasma itself is a valuable blood component that can be used or further processed for use in the treatment of patients with other disorders. Thus, it would be desirable to save the plasma for end uses other than platelet resuspension. Second, platelets often do not completely resuspend in plasma and/or complete resuspension of platelets in plasma occurs over an extended period of time.
Platelets that have not completely resuspended may be unsuitable for further processing or transfusion because of the presence of platelet aggregates (i.e. clumps of platelets). Platelet aggregates are undesirable because they can clog transfusion filters commonly used in platelet transfusions and/or platelet processing, such as filters designed for removal of white cells. Lower throughput because of clogged filters results in fewer platelets administered to a patient.
It is known, for example, that platelets will resuspend in saline solution (0.9% NaCl) and saline has been used to resuspend platelets in platelet washing procedures as shown and described in U.S. Pat. No. 5,462,752. Solutions that are primarily intended for the storage of platelets may also be useful for resuspending platelets. For example, the Platelet Additive Solutions (PAS) made by Baxter Healthcare Corporation are used for long term storage of platelets, but also may assist in the suspension of platelets. However, in addition to sodium chloride, these solutions include other components designed to help preserve the platelets such as (in the case of PAS I) sodium citrate, mannitol, phosphate, potassium chloride, See Eriksson, "Platelet concentrates in an Additive Solution Prepared from Pooled Buffy Coats," Vox Sang 1990:59:140-145 (1990) and (in the case of PAS II and PAS III) sodium acetate which serves as a nutrient for platelets. Thus, it would be desirable to resuspend platelet concentrates as completely as possible and in as short a time period as possible in a solution other than plasma or a platelet storage medium, and still provide a suspension of platelets suitable for storage or, if desired, readily available for transfusion to a patient.